The combination of a fluid pump and an electric motor into a single device has been the subject of patent literature for approximately the last sixty-five years. In spite of claims of reduced manufacturing costs, such a pump has yet to find popular application within the industrial world. The pumps disclosed in the literature are generally axial flow pumps or mixed flow pumps which appear to be restricted to high flow, low head applications. Multiple stage axial flow pumps are also known.
Other concerns with combined motor and pump units include the practical resolution of fluid seals and bearing application.
One example of a fluid flow device incorporating an integral motor and pump is disclosed by Richter in U.S. Pat. No. 3,276,382. In this patent, counter rotating impellers are provided which each form part of a tubular rotor that rotates inside a stator as shown in FIG. 3. The tubular rotor of the motor has anti-friction bearings to take into account both radial and thrust loads. An O-ring provides the seal between the tubular rotor and the casing.